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Related Concept Videos

Retrovirus Life Cycles01:10

Retrovirus Life Cycles

Retroviruses have a single-stranded RNA genome that undergoes a special form of replication. Once the retrovirus has entered the host cell, an enzyme called reverse transcriptase synthesizes double-stranded DNA from the retroviral RNA genome. This DNA copy of the genome is then integrated into the host’s genome inside the nucleus via an enzyme called integrase. Consequently, the retroviral genome is transcribed into RNA whenever the host’s genome is transcribed, allowing the retrovirus to...
Viral Recombination00:57

Viral Recombination

Cells are sometimes infected by more than one virus at once. When two viruses disassemble to expose their genomes for replication in the same cell, similar regions of their genomes can pair together and exchange sequences in a process called recombination. Alternatively, viruses with segmented genomes can swap segments in a process called reassortment.
Viral Mutations00:36

Viral Mutations

A mutation is a change in the sequence of bases of DNA or RNA in a genome. Some mutations occur during replication of the genome due to errors made by the polymerase enzymes that replicate DNA or RNA. Unlike DNA polymerase, RNA polymerase is prone to errors because it is not capable of “proofreading” its work. Viruses with RNA-based genomes, like HIV, therefore accrue mutations faster than viruses with DNA-based genomes. Because mutation and recombination provide the raw material for adaptive...
Retroviruses02:33

Retroviruses

Retroviruses and retrotransposons both insert copies of their genetic elements into the genome of the host cell. Thus, the viral genes are passed on when the host genome is replicated or translated. A typical retroviral DNA sequence contains 3-4 genes that encode the different proteins required for its structural assembly and function as a molecular parasite. This DNA is transcribed into a single mRNA, which is very similar in structure to conventional mRNAs, i.e., it is capped at the 5’...
LTR Retrotransposons03:08

LTR Retrotransposons

LTR retrotransposons are class I transposable elements with long terminal repeats flanking an internal coding region. These elements are less abundant in mammals compared to other class I transposable elements. About 8 percent of human genomic DNA comprises LTR retrotransposons. Some of the common examples of LTR retrotransposons are Ty elements in yeast and Copia elements in Drosophila.
The internal coding region of LTR retrotransposons and their mechanism of transposition closely resembles a...
Size and Structure of Viral Genomes01:26

Size and Structure of Viral Genomes

Viral genomes exhibit remarkable diversity in size, structure, and composition, influencing their replication strategies and interactions with host cells. These genomes consist of either DNA or RNA and may be linear or circular. Additionally, they can be single-stranded or double-stranded, with each configuration affecting how the virus propagates within a host. RNA viruses, for instance, generally have smaller genomes than DNA viruses, a factor that contributes to their high mutation rates and...

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Related Experiment Video

Updated: Jun 19, 2026

A Restriction Enzyme Based Cloning Method to Assess the In vitro Replication Capacity of HIV-1 Subtype C Gag-MJ4 Chimeric Viruses
14:23

A Restriction Enzyme Based Cloning Method to Assess the In vitro Replication Capacity of HIV-1 Subtype C Gag-MJ4 Chimeric Viruses

Published on: August 31, 2014

HIV evolution: CTL escape mutation and reversion after transmission.

A J Leslie1, K J Pfafferott, P Chetty

  • 1Department of Pediatrics, Fuffield Department of Medicine, Peter Medawar Building for Pathogen Research, University of Oxford, Oxford OX1 3SY, UK.

Nature Medicine
|February 11, 2004
PubMed
Summary
This summary is machine-generated.

Human immunodeficiency virus (HIV) evolution involves escape mutations. These mutations are not always accumulated, showing complex selection forces shape HIV population evolution.

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Pairwise Growth Competition Assay for Determining the Replication Fitness of Human Immunodeficiency Viruses
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Amplification of Near Full-length HIV-1 Proviruses for Next-Generation Sequencing
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Amplification of Near Full-length HIV-1 Proviruses for Next-Generation Sequencing

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Related Experiment Videos

Last Updated: Jun 19, 2026

A Restriction Enzyme Based Cloning Method to Assess the In vitro Replication Capacity of HIV-1 Subtype C Gag-MJ4 Chimeric Viruses
14:23

A Restriction Enzyme Based Cloning Method to Assess the In vitro Replication Capacity of HIV-1 Subtype C Gag-MJ4 Chimeric Viruses

Published on: August 31, 2014

Pairwise Growth Competition Assay for Determining the Replication Fitness of Human Immunodeficiency Viruses
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Pairwise Growth Competition Assay for Determining the Replication Fitness of Human Immunodeficiency Viruses

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Amplification of Near Full-length HIV-1 Proviruses for Next-Generation Sequencing
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Amplification of Near Full-length HIV-1 Proviruses for Next-Generation Sequencing

Published on: October 16, 2018

Area of Science:

  • Immunology
  • Virology
  • Population Genetics

Background:

  • Within-patient human immunodeficiency virus (HIV) evolution is driven by cytotoxic T-lymphocyte (CTL) escape.
  • The impact of intrapatient escape mutations on population-level HIV evolution remains unclear.

Purpose of the Study:

  • To investigate whether intrapatient accumulation of HIV escape mutations translates to population-level evolution.
  • To analyze the role of specific human leukocyte antigen (HLA) alleles in shaping HIV evolution.

Main Methods:

  • Studied over 300 patients from HIV-1 B and C clades.
  • Focused on HLA-B57 and HLA-B5801 alleles, known for strong CTL selection pressure.
  • Tracked the transmission and reversion of CTL escape mutations.

Main Results:

  • A CTL escape mutation reverted to wild-type after transmission to individuals lacking HLA-B57/5801.
  • Another escape mutation within the same epitope was maintained after transmission.
  • Demonstrated that HIV escape mutation accumulation is not inevitable.

Conclusions:

  • HIV evolution is shaped by complex, epitope-specific selection pressures.
  • CTL-mediated positive selection and virus-mediated purifying selection interact to influence population-level HIV diversity.